Many conventional printers are provided with relatively complex paper-handling devices, including input paper trays and output paper stackers which each have their own motors and internal control logic. Under certain conditions, it is important for the paper-handling devices (including these input paper trays and output paper stackers) to be placed into a "homing mode" so that the main printer is assured that the paper-handling devices are being set into a particular known configuration. This is almost always the case when a printer is first turned on, or is otherwise put through a reset cycle.
Some of the more complex printers can be provided with optional paper-handling devices that can be added to the printer, in which individual motor drives are provided with such paper-handling devices that are controlled by logic commands from the print engine or some other control logic that is derived from the main printer system controller. In some situations, the print engine can communicate to the paper-handling devices using logic signals that are communicated over separate physical electrical conductors. Alternatively, the control signals could be transmitted over a dedicated communications bus or communications channel, that would act as a type of multiplexer at the printer control end and a de-multiplexer at the paper-handling device end, so that when a particular type of signal is sent, the correct paper-handling device is made aware that it is now supposed to become activated.
Another type of communications scheme could be one where certain coded messages are sent over a communications bus that acts much as a data or address bus in a microprocessor-memory system, and at the receiving end, the correct "address", once deciphered, would then cause the paper-handling device to become activated. Of course, more than one type of message could be directed at the same paper-handling device, so that a homing command would be interpreted as such, as opposed to some other type of energization or de-energization command.
In some conventional printers, upon a reset or upon a warmup situation, all of the paper-handling devices could be simultaneously placed into their homing modes. If that occurred, then multiple motors or motor-driven mechanisms would turn on concurrently, and the instantaneous power consumption would suddenly jump to a very high value with respect to the printer's power supply output current rating. This situation would be exacerbated if the fuser would also be energized during that same time interval by DC power. Therefore, the printer's power supply output rating was required to be quite large as compared to its "normal" output loading during standard operating conditions of the printer. This peak power demand requirement would occur when the paper-handling devices were simultaneously energized regardless of whether or not each paper-handling device had its own individual motor, or whether there was a much larger motor that supplied a separate mechanical drive to multiple paper-handling devices. The situation in which each paper-handling device has its own individual motor is probably the worst case scenario, because each of the motors that initially becomes energized will have a relatively large instantaneous "inrush" current demand as it begins to turn from zero RPM (revolutions per minute) and then accelerates toward its full-speed RPM, which draws a large current surge from the DC power supply to overcome its torque requirements when driving its associated load, especially during the initial moments of rotation.
Reducing peak power consumption in electrical systems has been practiced for many years with respect to industrial plants and commercial buildings. For example, electrical load controllers are often provided that include time schedules for particular pieces of electrically-energized equipment so that certain equipment may be turned off during certain times during the day. These time schedules might also include a parameter which specifies a certain maximum amount of time where the particular piece of electrical equipment may be continuously turned off, however, that piece of equipment must then be allowed to again be energized so it can perform its intended function without causing a major detrimental effect to its overall system. For example, in a system which requires electrical motors to provide the driving force for air pumps or air compressors, or to provide the driving force for a pressurized water system, it may be possible to turn off one or more electric motors while other similar motors remain running, thereby reducing the peak power consumption of the system. However, the overall performance of that system will become significantly degraded if the situation is allowed to continue operating under that condition indefinitely, so one of the air or water pumps must be allowed to be added to this system after a certain time interval, during which some other unrelated system may be required to shut down one of its electrical motors.
Other ways of reducing the peak electrical demand of a control system can be used in situations where energy may be stored in some manner as potential energy in a form other than electricity. One such example is where a chilled water system "pre-cools" a building during the early morning hours when the rest of the utility company's electrical distribution system is in a relatively minimal power consumption operating state. This pre-cooling is achieved by causing certain interior spaces (such as large conference rooms of a convention center) to be cooled to a much lower temperature than is normally required and then later allowing this very cool room to gradually warm up during the peak electrical demand portions of the day by not having the chilled water system provide as much cooling as would otherwise be required without this pre-cooling step.
Some of the power consumption control systems have been patented, including U.S. Pat. No. 4,210,901 (by Whyte), which discloses a distribution network power line communication system that is divided into addressable communication zones defined by signal repeaters located at spaced intervals along the distribution network. The repeaters are connected between the primary and grounded neutral conductors of the primary distribution network. Each repeater has a unique address that can be interrogated from a central communication terminal. The messages are transmitted over high-voltage power lines, and once a repeater and a remote terminal device has been selected by the unique address, a code can be transmitted to the remote terminal that indicates which automatic function is to be performed by the remote terminal.
U.S. Pat. No. 4,454,509 (by Buennagel) discloses a load management system which includes a central message generator and a plurality of addressable remote load controllers that, in response to transmitted messages, selectively connect and disconnect high power deferrable loads. The load controllers have means for translating coded tone input signals into digital data. The message format includes two code sets, a zone code set and a command/address code set. All load controllers having a common zone identifier are responsive to a "scram" instruction message that is directed to that zone. This scram message is designed to be able to disconnect a large number of deferrable electrical loads in a short time period to avoid a blackout.
U.S. Pat. No. 4,949,359 (by Voillat) discloses a system that transmits data between a master station and a plurality of slave stations where there is a simultaneous return of data back to the master station, and this is accomplished on a bus having only two conductors. The digital signals sent by the master station to the slave stations are also control signals that feed power to the slave stations. The data bits of these signals have a wave form shape such that there are "dead zones" during which the signals have no effect and during which the transmission may be interrupted by putting a high impedance on one of the conductors, which allows a momentary alteration of the signal. The presence or absence of such an alteration constitutes data that is being transmitted from a slave station to the master station.
U.S. Pat. No. 5,287,353 (by Buda) discloses a communication system between a microprocessor and a network of several remote input/output repeater modules that control various devices. A synchronous serial communications protocol is used when a microprocessor transmits data packets sent to the repeater modules. The data packets have an output data byte for each of the repeaters that sets the state of the output devices connected to the repeater modules.
U.S. Pat. No. 4,075,699 (by Schneider) discloses a power controlling/load shedding system that includes power consumption metering. A central processing unit (CPU) includes a memory that stores a data table that characterizes each electrical load in the system under each of the hierarchy of operational levels. Circuits are also provided to turn local and remote loads on or off in response to CPU-issued commands. The CPU can project energy consumption over a monitoring interval. If power must be shed, loads are examined seriatim and the loads are selectively shed on a priority basis as required.
Some of the conventional energy management control systems are designed to reduce the overall power consumption of homes. An example of this is U.S. Pat. No. 4,847,781 (by Brown), which discloses an energy management system that uses a central control unit to provide energy management signals to a plurality of subscriber units. More specifically, the central control unit is provided by the electrical utility company, the subscriber units are placed in homes, and the energy management signals are transmitted over TV cables, power lines, telephone lines, or free space radio frequency transmissions. Certain appliances within the homes will be managed with regard to whether they are allowed to operate, or to be turned off during certain time intervals. Each appliance will include a responder unit so that it can receive messages from the central control unit. Each subscriber can enter a particular code to use a schedule of on- or off-times for each of the responders. These codes are supplied to the subscribers, and the responder will then respond only to codes that conform to the code set used in the encoding devices within each responder.
Another patent that discloses a conventional energy management control system to reduce the overall power consumption of homes is U.S. Pat. No. 4,899,131 (by Wilk), which discloses a control system having a central unit that applies a DC operating current and control signals to a two line bus. The central unit applies a direct current to the bus, as well as an electrical signal. The system is designed to be a local control system for loads in a home, and can use one-way communication to automatically switch a load on or off. It can also use two-way communication, using an alarm loop which can detect a change in the direct current level on the bus, wherein a current response constitutes a message from a peripheral unit to the central unit. The change in current of the two-wire bus can be measured by a series resistor, as well as by other devices. A "manual control unit" (such as a keyboard) can be used to load the bus, and can be used to inhibit such loading of the bus. Control signals are sent to terminal units, which are used to either connect or disconnect one of the system loads.
U.S. Pat. No. 5,600,310 (by Whipple) discloses a household appliance having a serial bus control system that includes a system controller and a plurality of slave nodes. Each slave node is a sensor or an actuator, and is responsive to a particular slave node address code generated by a master communications module at the system controller. The master communications module includes an interrogation circuit that transmits digital messages to the slave nodes and receives sensor signals from slave nodes. The system controller can sense the condition of the appliance and generate control signals to optimize energy efficiency. This includes the ability to power down the control circuitry to reduce energy consumption during periods when the appliance is idle. When the power-down circuitry is used, it typically slows the update periodicity of the controller, and power is shut down to unused peripherals.
The prior art also includes attempts to limit the peak power requirements of certain types of printers. One example of this is disclosed in U.S. Pat. No. 5,349,905 (by Taylor), which discloses a thermal ink jet printer that uses a copy speed feed control for reducing peak power requirements. The incoming print data is evaluated by the printer to determine the image density, or in an alternate embodiment the excess power consumption to dry the ink in a dryer is measured. The speed of the sheet transport system is controlled in accordance with the image density so that the speed of the sheet at the printer and/or at the dryer is reduced at high image densities. In the first mode of operation, the image density is evaluated (based on raster pixel density), and the result provides a signal to a servo-control system that sets the speed of the variable-speed drive motor that controls the speed of the belt that transports the paper through the printer. In this manner, it is possible to have each sheet of a print job travel through the printer at varying rates of speed depending upon the print density in each area of the sheet. In the alternative embodiment, a microwave dryer is operated at a fixed power output. The amount of power in excess of that needed to dry the ink on the page is absorbed in a dummy load, and if very little power is being absorbed in the dummy load, this is an indication that the dryer is operating close to optimum speed for the density of printing being dried. If the power dissipated in the dummy load is high, that indicates the amount of ink to be dried is low, and the speed of the belt can be increased.
Another example patent is U.S. Pat. No. 5,317,366 (by Koshi), which controls the AC power provided to multiple electronic photo printers. An AC branch circuit power source is described as having only a 15 Ampere capacity (e.g., at 120 VAC). whereas the power consumption of each printer is in the range of 7 to 8 Amperes. The heat rollers ordinarily consume the greater part of the power in the electronic photo printer, and it is important to not have all of the photo printers energized simultaneously as far as providing power to their individual heat rollers. Otherwise, the power consumption will exceed the 15 Ampere capacity of the branch circuit, and a circuit breaker will open, disabling all of the photo printers.
In one example of a 7 Ampere printer, Koshi will allow two of the printers to be turned on simultaneously, but will prevent the next printer from energizing its heat roller until after the time interval has expired for a pulse of current being supplied to one of the previously energized printers, thereby allowing the next printer to eventually have its heat roller energized without causing the circuit breaker to open. To delay the power supply from energizing the heat roller of the "next" photo printer, the power supply voltage is measured at the printer just before it is time to energize its heat roller. If the voltage has fallen below a certain threshold, that is an indication that a large amount of current is already being consumed by the other photo printers. In this circumstance, the "next" printer will not have its heat roller energized just yet. Once the pulse current has been turned off to one of the previously powered printers, the voltage level will rise above the threshold, and the "next" printer can then have its heat roller energized. The printer having its heat roller energization delayed will not be able to instantly begin operations, however, it will only be delayed by a small amount of time, and this benefits the overall system by preventing a power outage when the circuit breaker would open where the Koshi invention was not being used.
It would be desirable to provide a printer that purposefully controls the initial energization of its various electrically-powered devices, and particularly controls the paper-handling devices that contain their own individual electric motor. It is even more important to have the printer control such devices during a homing operation, which would generally occur after a power on reset of the printer.